Photocatalyst sheet

ABSTRACT

A photocatalytic sheet which has a base made of polymeric organic compound, that is not decomposed by a photocatalytic function, and also hardly loses the photocatalytic function after washing and is capable of providing the photocatalytic function even in an environment without sufficient ultraviolet radiation from outside. Using a fiber, a filament, a yarn made of fibers or filaments, a ribbon, a knitted fabric, a woven fabric, a nonwoven fabric, or a film as the base, a base protective layer is formed on a part of the base, which is made of the polymeric organic compound, and a photocatalytic semiconductor layer is formed on the entire surface of the base including the base protective layer.

TECHNICAL FIELD

The present invention relates to a sheet of knitted fabric, wovenfabric, nonwoven fabric, etc., which is capable of decomposing harmfulorganic compounds in gas or liquid by a photocatalytic function of metaloxide, and thereby rendering the gas or liquid harmless or sterilizingthe same.

BACKGROUND ART

Many metal oxides such as titanium oxide (TiO₂) are called opticalsemiconductors since electrons on their surface are made movablerelatively freely when they are excited by ultraviolet rays. The opticalsemiconductor has a photocatalytic function of oxidizing or deoxidizinga substance in contact with a surface of the semiconductor by theelectrons which are rendered freely movable by the excitation.

The photocatalytic function is utilized in a daily life to attain aneffect of deodorization or sterilization. For example, in order topurify the air in a room of a house or facilities open to general publicsuch as hotels, public buildings and hospitals, the photocatalyticfunction is given to materials of interiors including ceilings andwalls, or the photocatalytic semiconductor is retained in curtains whichare often exposed to ultraviolet radiation of the sunlight. Thus, theair which rises to circulate in the room when heated by the sunlightcomes into contact with sheets of these materials, so that odors in theroom and volatile organic compounds (VOC) contained in adhesives inbackings of the interior materials are effectively removed.

The woven fabrics for the interior materials and the curtains, as wellas filters in various devices, medical gauze, moistened tissue andnonwoven fabrics such as artificial leather have a large number of gapsbetween their fibers and thus are multi-surface objects, and hygienic,medical or deodorizing effect can advantageously be obtained byimparting the photocatalytic function to these objects.

These advantageous effects can be achieved on condition that the fiberor fabric itself, which is a base for retaining the photocatalyticsemiconductor, should not be decomposed by the photocatalytic function.However, the photocatalytic function is originally a function ofdecomposing the polymeric organic compounds by theoxidization/deoxidization action of the photocatalytic semiconductorwhich is excited by irradiation of ultraviolet rays. Therefore, noproblem arises if the base retaining the photocatalytic semiconductor ismade of an inorganic material such as metallic fibers or glass fibers,but in the case where the base is made of fibers of polymeric organiccompound such as natural fibers or synthetic resin fibers, the baseitself is decomposed and deteriorated with lapse of time (deteriorationby photocatalysis).

Further, polymeric organic compounds are decomposed and deterioratedalso by ultraviolet rays (photochemical deterioration). Most of theexternal ultraviolet rays falling on the base having the photocatalyticsemiconductor layer on the surface thereof are absorbed at thephotocatalytic semiconductor layer, but the remaining rays reach thebase.

As a conventional sheet having the photocatalytic function, there isknown a sheet in which particles of white pigment, each retainingparticles of photocatalytic semiconductor on its surface, are containedor filled in an air-permeable sheet as proposed in Japanese Laid-OpenPatent Publication No. 7-299354. However, this sheet with a uniquestructure lacks versatility and it is not possible to make a softmaterial such as gauze by using the sheet.

Japanese Laid-Open Patent Publication No. 7-316342 discloses thatsynthetic resin containing particles of photocatalytic semiconductor isformed into a sheet for wall materials, floor materials, and variousbags. However, when the photocatalytic semiconductor particles are thuskneaded into the base, the photocatalytic function cannot be fullyachieved. Also, the technique disclosed in this publication cannot beapplied to fabric made of natural fibers which cannot be kneaded.

Further, Japanese Laid-Open Patent Publication No. 8-1010 discloses anadhesive sheet having a layer of fine particles of oxide semiconductoron one surface thereof, an adhesive layer as an intermediate layer, anda separating layer on the other surface thereof. This sheet is intendedto use at locations where it is difficult to fix photocatalyticsemiconductor particles, such as walls or ceilings, and also cannot beapplied to soft material such as gauze.

In the conventional sheets of these types, no consideration is given toprevention or suppression of the deterioration by photocatalysis and thephotochemical deterioration. Also, the washability of the sheet forreuse and the use of the sheet in an environment without sufficientultraviolet radiation, such as in the nighttime or in a dark room, arenot taken into account.

DISCLOSURE OF INVENTION

An object of the present invention is providing a photocatalytic sheetwhich has a base, made of polymeric organic compound and retainingphotocatalytic semiconductor, that is not decomposed by a photocatalyticfunction, and thus can withstand long-term use. The object includesproviding a photocatalytic sheet which hardly loses the photocatalyticfunction even if washed, and is capable of providing the photocatalyticfunction even in an environment without sufficient ultraviolet radiationfrom outside.

A photocatalytic sheet according to the present invention comprises abase having a part made of polymeric organic compound; a base protectivelayer formed on a surface of the part made of polymeric organic compoundin the base, for intercepting photocatalytic function; and aphotocatalytic semiconductor layer formed on an entire surface of thebase including said base protective layer.

The base includes a fiber, a filament, a yarn made of fibers orfilaments, a ribbon, a knitted fabric, a woven fabric, a nonwovenfabric, and a film made of synthetic resin.

The base protective layer may comprise noncrystalline titanium peroxideparticles or titanium oxide particles inactivated with respect tophotocatalytic function. The photocatalytic semiconductor layer maycomprise constituted by titanium oxide particles.

The base may retain a spontaneous emission-type ultraviolet radiatingmaterial or a light storage-type ultraviolet radiating material. In thiscase, the compositions of the ultraviolet radiating material and thephotocatalytic semiconductor layer are adjusted so that a peak region ofwavelength spectrum of light radiated from the ultraviolet radiatingmaterial is shifted from a peak region of wavelength spectrum of lightto be absorbed by the polymeric organic compound, and overlaps at leastin part with a peak region of light absorption spectrum of thephotocatalytic semiconductor layer.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of a fiber having a base protective layer anda photocatalytic semiconductor layer formed on a base;

FIG. 2 is a sectional view of a fiber having the base protective layerand the photocatalytic semiconductor layer formed on a base containingan ultraviolet radiating material;

FIG. 3 is a sectional view of a fiber having the base protective layerand the photocatalytic semiconductor layer formed on a base in whichregions containing the ultraviolet radiating material are arrangedradially;

FIG. 4 is a sectional view of a fiber having the base protective layerand the photocatalytic semiconductor layer formed on a base in which aregion containing the ultraviolet radiating material is arrangedannularly;

FIG. 5 is a sectional view of a twisted yarn having the base protectivelayer and the photocatalytic semiconductor layer formed on naturalfibers, and synthetic fibers admixed with an ultraviolet radiatingmaterial;

FIG. 6 is a schematic front view of an experimental device; and

FIG. 7 is a schematic plan view of the experimental device of FIG. 6with black-light lamps omitted.

BEST MODE OF CARRYING OUT THE INVENTION

A photocatalytic sheet according to the present invention may take theform of a knitted fabric, a woven fabric, a nonwoven fabric, or a film.The material of the sheet may be natural fibers such as hemp, cotton andwool, and also synthetic fibers (including filaments) or synthetic resinof polyester, rayon, nylon, polypropylene, vinyl, acetate, acrylic, etc.The sheet except the film is formed through the steps of fibers, spunyarns, twisted yarns, or ribbons.

Also, metallic fibers or glass fibers may be used, and a single sheetmay be formed using a plurality of materials. Depending on the use ofthe sheet, moreover, paper or artificial leather may be used. The sheetneeds to have a decorative element and sufficient strength when used forthe purposes of interior materials or accessories, and needs to haveflexibility for clothing or hygienic purposes.

A base protective layer is constituted by a layer of noncrystallinetitanium peroxide particles formed using an aqueous solution of titaniumperoxide, a peroxotitanic acid, a peroxotitanic acid containing an oxideof metal other than titanium, etc., or by a layer of titanium oxideparticles inactivated in respect of photocatalytic function. The layerobtained in this manner has no photocatalytic function and thus does notdecompose the base.

The layer of noncrystalline titanium peroxide particles can be formed onthe surface of the base in the following manner, for example.

A fabric as the base which has been subjected to dyeing as a final stepis sprayed with or dipped into an aqueous solution of titanium peroxideshowing an intermediate property between sol and gel states, and aftersurplus solution is removed, the fabric is dried and then heated so asto fix the titanium peroxide at a temperature of 200° C. or less, takingthe heat resisting temperature of the base into consideration.

The surface of the base may alternatively be coated with an aqueoussolution of peroxotitanic acid by, for example, dipping as in theaforementioned manner, dried and then heated for fixing at a temperatureof 200° C. or less.

In this manner, a layer of noncrystalline titanium peroxide particles isformed on the surface of the base.

In the case of using peroxotitanic acid, if the heating temperature ishigher than 200° C., the resultant noncrystalline titanium peroxideparticles show a property similar to that of titanium oxide of anatasetype and have a photocatalytic function.

As an alternative method, a raw resin for forming fibers as the base maybe ejected from a nozzle into an aqueous solution of peroxotitanic acidso that a thin film of noncrystalline titanium peroxide particles may beformed on the surface of each fiber. Also in this case, the fibers aredried and then heated so as to fix the titanium peroxide at atemperature of 200° C. or less. The fixing may be performed afterspinning, after twisting, or after weaving.

The layer of titanium oxide inactivated in respect of the photocatalyticfunction may be formed on the surface of the base in the followingmanner, for example.

An ionic surface-active agent is mixed in a sol of titanium oxide ofanatase type such that the surface-active agent accounts for 1 wt % ormore with respect to the concentration of the titanium oxide (TiO₂) inthe sol, thereby inactivating the photocatalytic function of thetitanium oxide, and then the base is sprayed with, dipped into, orapplied with the sol. Subsequently, the base is dried and then heatedfor fixing the titanium oxide.

A photocatalytic semiconductor layer is formed on the surface of thebase treated in this manner, and in this case, even if thephotocatalytic semiconductor is excited upon exposure to ultravioletradiation, electrons moving toward the surface of the base combine withions of the ionic surface-active agent contained in the base protectivelayer, thus preventing oxidation-reduction of the surface of the base.Consequently, the base is not affected by the photocatalytic functionand thus can be protected.

The base on which the photocatalytic semiconductor is to be retained isnot limited to the form of knitted fabric, woven fabric, nonwoven fabricor film, but may be of various forms obtained in respective steps of thesheet production process, such as fibers, spun yarns, twisted yarns, orribbons. Particles of photocatalytic semiconductor may be affixed atearly stages of the process to fibers or yarns, for example, oncondition that no difficulty arises in performing the treatment, inwhich case the photocatalytic semiconductor is firmly fixed to theresultant sheet and the photocatalytic function can be retained even ifthe sheet is washed several times.

Namely, as the base retaining photocatalytic semiconductor for impartingthe photocatalytic function to the sheet, one or some of the formsincluding fiber, filament, yarn, ribbon, knitted fabric, woven fabric,nonwoven fabric and film may be selected depending on the purpose.

The layer of noncrystalline titanium peroxide particles or the layer ofinactivated titanium oxide needs to be formed on natural fibers orsynthetic resin fibers. Therefore, in cases where inorganic fibers andorganic fibers cannot be treated separately, as in producing a filter ofnonwoven fabric by entangling glass fibers and synthetic resin fibers,it is advisable to treat the fibers as the base, that is, to perform thestep of forming the base protective layer on the fibers, and then formthe fibers into nonwoven fabric. Alternatively, however, after anonwoven fabric is formed, it may be subjected in its entirety to thestep of forming the base protective layer.

The photocatalytic semiconductor to be used may be TiO₂, ZnO, SrTiO₃,CdS, CdO, CaP, InP, In₂ O₃, CaAs, BaTiO₃, K₂ NbO₃, Fe₂ O₃, Ta₂ O₅, WO₃,SaO₂, Bi₂ O₃, NiO, CU₂ O, SiC, SiO₂, MoS₂, MoS₃, InPb, RuO₂, or CeO₂.

These photocatalytic semiconductors absorb ultraviolet radiation with awavelength of 50 to 400 nm, which is slightly shorter than that ofvisible light. Some of the photocatalytic semiconductors, however, havean absorption wavelength falling within the range of visible light. Forexample, SiC has an absorption wavelength of 413 nm, CdS has anabsorption wavelength of 496 nm, and Fe₂ O₃ has an absorptionwavelengthof 539 nm.

Thus, the wavelength of light with which photocatalytic semiconductorsare excited varies depending on their type, and therefore, a suitablephotocatalytic semiconductor may be selected in accordance with theintended use or the emission spectrum characteristic of the source ofultraviolet radiation, or multiple types of photocatalyticsemiconductors may be used in combination for adjustment.

Also, by adding an inorganic pigment or a metal to thereby adjust thecomposition or by controlling the heating step in the productionprocess, it is possible to shift the wavelength of ultraviolet radiation(absorption band) that is required to provide the photocatalyticfunction. For example, if a small quantity of CrO₃ is added to TiO₂,then the absorption band shifts toward a longer wavelength side.

As an additive for providing a complementary function such as mildewresistance, sterilization, etc., Pt, Ag, Rh, RuO₂, Nb, Cu, Sn, NiO andthe like may be used in combination.

Among the photocatalytic semiconductors mentioned above, TiO₂ (titaniumoxide) is commercially available, harmless to the human body,inexpensive, and easy to use. "ST-01" (trade name; manufactured byIshihara Sangyo Kaisha, Ltd.) is supplied in the form of powder, while"TO SOL" (trade name; manufactured by Tanaka Transfer Printing Co.,Ltd.) and "STS-01" (trade name; manufactured by Ishihara Sangyo Kaisha,Ltd.) are supplied in the form of sol. TiO₂ constituting the powder orsol has a very small particle diameter of 7 to 20 nm.

To fix the photocatalytic semiconductor on the base, various means suchas spraying, applying, dipping or sputtering can be employed, and asuitable means may be selected depending on the base type. However,since the sheet to be obtained is required to withstand reuse orwashing, the base with the photocatalytic semiconductor thereon issubjected to heat treatment. In the case of TiO₂, the temperature forthe fixing ranges relatively wide from 50 to 500° C., but in the case ofusing peroxotitanic acid as the base protective layer, the fixing isperformed at a temperature of 200° C. or less. As regards the heatresistance of fibers presently on the market, rayon, acetate, nylon andpolyester have heat resisting temperatures of 260° C. or less, 200° C.or less, 180° C. or less, and 230° C. or less, respectively, and thuscan sufficiently withstand coating with heat applied thereto.

With the photocatalytic sheet produced in this manner, as ultravioletrays from fluorescent lamps in the room or ultraviolet rays in thesunlight are received, the photocatalytic semiconductor retained on thesheet is excited and decomposes harmful organic matter by means ofoxidation-reduction, thus providing a deodorizing effect, an airpurifying effect, a sterilizing effect, etc.

Especially in the case where the sheet is used as a curtain which isarranged at an opening and is liable to receive the sunlight, the air inthe room, which rises and circulates within the room as it is heated,efficiently comes into contact with the photocatalytic semiconductor,whereby odor in the room and volatile organic compounds (VOC) containedin building materials, adhesives, etc. can be removed.

Also, where the sheet is used for medical articles such as sterilizinggauze or is used for sanitary articles such as moistened tissue,infections can be effectively prevented.

The base may retain also an ultraviolet radiating material.

With a photocatalytic sheet having an ultraviolet radiating materialmixed in the base, ultraviolet rays necessary for exciting thephotocatalytic semiconductor are supplied by the photocatalytic sheetper se, so that the photocatalytic function can be obtained andmaintained even while no or only little ultraviolet radiation isavailable from outside, such as in the nighttime or within doors.

Ultraviolet radiating materials include a spontaneous emission type anda light storage type. The spontaneous emission-type ultravioletradiating material (spontaneous emission-type luminous ceramic) is amaterial that consumes its internal energy to emit light by itself andutilizes radioactive decay of radium or promethium, and an emissionspectrum thereof includes an ultraviolet region. Presently, a lumpobtained by solidifying refined powder of rocks containing such amaterial is again crushed and the thus-obtained crushed particles areused. The particle diameter is 20 to 50 μm.

The light storage-type ultraviolet radiating material (lightstorage-type luminous ceramic) is a material that obtains energy fromoutside and emits light by releasing the energy stored therein, and anemission spectrum thereof includes an ultraviolet region. As such amaterial, "LUMINOVA" (trade name; manufactured by Nemoto & Company Ltd.)and "KEPRUS" (trade name; manufactured by Next Eye Co., Ltd.) arecommercially available. These products contain strontium aluminate(SrAl₂ O₄) as a main component, besides high-purity alumina, strontiumcarbonate, europium, dysprosium, etc.

If the light storage-type ultraviolet radiating material is exposed tosufficiently intense ultraviolet rays from outside for 4 to 30 minutes,absorption of external energy for light emission becomes saturated, andeven if the supply of external energy is cut off thereafter, thematerial keeps emitting light for about 1000 minutes, thus irradiatingthe photocatalytic semiconductor with ultraviolet rays. In the case of"LUMINOVA," for example, the spectrum of emitted ultraviolet rays has awavelength peak in the vicinity of 440 to 530 nm, but includes also awavelength region in which ordinary photocatalytic semiconductors areexcited.

Some of the ultraviolet radiating materials greatly lower in capacity onabsorbing moisture; therefore, they are preferably mixed beforehand inthe base so that they may not come into direct contact with moisture, oncondition that the base has transparency to ultraviolet radiation. Inthe case where natural fibers are used, synthetic resin admixed with theultraviolet radiating material is sprayed on the base for coating beforethe base protective layer is formed.

The ultraviolet radiating material is retained on the sheet chiefly bymeans of adhesion or fixing to the surface of the base, but in the caseof synthetic resin fibers or a synthetic resin film, the ultravioletradiating material may be mixed in the base. Also, where the fibers usedare synthetic resin filaments, the ultraviolet radiating material may bemixed in some of radially segmented regions as viewed in section, or bemixed in ring form so as to constitute the outermost layer as viewed insection.

Such filaments are produced by extruding a raw resin mixed with theultraviolet radiating material and a raw resin having no ultravioletradiating material mixed therein from separate nozzles into the air or acooling liquid such as organic solvent, water or the like, and bringingthe extruded resins into close contact with each other before they set.

In the case of natural fibers, particles of the ultraviolet radiatingmaterial cannot be mixed in the fibers themselves; therefore, in thestep of twisting yarns, the natural fibers and synthetic resin fibersadmixed with the ultraviolet radiating material are twisted together.

The base is subject to photocatalytic deterioration caused due to thephotocatalytic function of the photocatalytic semiconductor as well asto photochemical deterioration caused by ultraviolet rays, as mentionedabove. Suppression of the photocatalytic deterioration is already statedabove.

The photochemical deterioration is suppressed by utilizing the fact thatresins are different from one another as to the rate of photochemicaldeterioration and the wavelength with which they are most liable to bedeteriorated. In typical synthetic resins, the wavelength that causesthe greatest deterioration is 318 nm for polyester, 300 nm forpolyproplylene, 285 to 305 nm and 330 to 360 nm for polycarbonate, and300 nm for polyethylene.

Namely, to prevent the photochemical deterioration, an ultravioletradiating material is selected of which the peak of emission wavelengthspectrum differs from the wavelength that causes the greatestdeterioration of the resin used. Also, the excitation wavelength of thephotocatalytic semiconductor retained on the base is made different fromthe wavelength which causes the greatest deterioration of the syntheticresin. Needless to say, the addition of an ultraviolet ray absorbingmaterial, such as 2-hydroxybenzophene or triazole, to the base iseffective in preventing the photochemical deterioration.

The photocatalytic sheet according to the present invention will be nowdescribed with reference to specific examples.

EXAMPLE 1

Using, as a base, a nonwoven fabric (4880C, from Shinwa Co. Ltd.)obtained by bonding polyester fibers and rayon fibers together by anacrylic binder, the base was first washed in tap water and then in purewater, and was dried at 70° C. Subsequently, the base was dipped into asol of titanium peroxide (viscous sol containing 0.3 wt % TiO₃ andhaving pH 5) at room temperature (23.8° C.), and after surplus sol wasremoved, the base was placed in a space in which titanium oxide powder(ST-01, from Ishihara Sangyo Kaisha, Ltd.) was floating, to allowtitanium oxide particles to adhere to the entire surface of the base,followed by drying.

The base obtained in this manner was then half-dried in an atmosphere of50° C., and the entire surface thereof was ironed at 120 to 150° C. tofix the titanium oxide particles, thereby obtaining a final product.

The final product was light yellowish white in color as a whole, andalthough the gaps between the fibers constituting the nonwoven fabricwere slightly clogged, the external appearance looked almost the same asthat before the treatment. FIG. 1 is a schematic enlarged sectional viewof a fiber constituting the fabric. As shown in the figure, the baseprotective layer 2 constituted by a layer of noncrystalline titaniumperoxide particles is formed on the surface of the fiber 1 located atthe center, and the photocatalytic semiconductor layer 3 is formed onthe surface of the base protective layer 2.

The final product was placed like wallpaper in the space of an ordinaryroom, and after the product was left to stand for two months, theproduct was pulled lengthwise and widthwise and was bent, but noabnormality was found as to strength and other properties. Thisexperiment is being continued on a long-term basis, to observedeterioration of the base (photocatalytic deterioration andphotochemical deterioration).

The oxidation-reduction capacity is summarized hereinafter asexperimental results.

EXAMPLE 2

Using, as a base, a woven fabric (DEOLIA; from Nippon Fisba K. K.) madeof mixed fibers containing 50% cotton and 50% polyester, the base wasfirst washed in tap water and then in pure water, and was dried at 70°C., as in Example 1. Subsequently, the base was dipped into a sol oftitanium peroxide (sol containing 0.5 wt % TiO₃ and having pH 6.4) atroom temperature (23.8° C.), and after surplus sol was removed, the basewas placed in a space in which titanium oxide powder (ST-01; fromIshihara Sangyo Kaisha, Ltd.) was floating, to allow titanium oxideparticles to adhere to the entire surface of the woven fabric, followedby drying.

The base obtained in this manner was then half-dried in an atmosphere of50° C., and the entire surface thereof was ironed at 120 to 150° C. tofix the titanium oxide particles, thereby obtaining a final product.

Each fiber had a cross section similar to that shown in the schematicdiagram of FIG. 1.

The final product was light yellowish white in color as a whole, and theexternal appearance thereof looked almost the same as that before thetreatment. The final product was placed like wallpaper in the space ofan ordinary room, and after the product was left to stand for twomonths, the product was pulled lengthwise and widthwise and was bent,but no abnormality was found as to strength and other properties. Thisexperiment is being continued on a long-term basis, to observedeterioration of the base (photocatalytic deterioration andphotochemical deterioration).

The oxidation-reduction capacity is summarized hereinafter asexperimental results.

EXAMPLE 3

Using a woven fabric (DUFY; from Nippon Fisba K. K.) of 100% cotton as abase, the base was first washed in tap water and then in pure water, andwas dried at 70° C., as in Example 1. Subsequently, the base was dippedinto a mixture of a sol of titanium peroxide (sol containing 1.76 wt %TiO₃ and having pH 6.0) and a sol of titanium oxide (TO from TanakaTransfer Printing Co., Ltd.; 3.94 wt % titanium oxide; pH 8.1) at roomtemperature (23.8° C.). After surplus sol was removed, the base wasdried in an atmosphere of 50° C.

In this case, a layer constituted by a mixture of titanium peroxideparticles and titanium oxide particles is formed on the surface of eachfiber; since the sol of titanium peroxide has more excellentspreadability with respect to the surface of the fiber, a layer oftitanium peroxide particles is formed near the surface of the fiberwhile a layer of titanium oxide is formed on the outermost side.Although the available photocatalytic capacity is somewhat low, it isunnecessary to perform an additional step for the adhesion of titaniumoxide powder.

Subsequently, the entire surface of the base was ironed at 120 to 150°C. to fix the layer of titanium oxide particles and titanium peroxideparticles, thereby obtaining a final product.

The external appearance of the final product was almost the same as thatbefore the treatment. The final product was placed like wallpaper in thespace of an ordinary room, and after the product was left to stand fortwo months, the product was pulled lengthwise and widthwise and wasbent, but no abnormality was found as to strength and other properties.This experiment is still being continued to observe deterioration of thebase (photocatalytic deterioration and photochemical deterioration) on along-term basis.

The oxidation-reduction capacity is summarized hereinafter asexperimental results.

FIGS. 2 to 4 each show an example wherein "LUMINOVA" as the lightstorage-type ultraviolet radiating material is mixed in a polyesterfiber 1, in accordance with Examples 1 to 3 described above. In theexample of FIG. 2, the ultraviolet radiating material is mixed in thewhole of the fiber 1, in the example of FIG. 3, the ultravioletradiating material is mixed in a plurality of radially segmented regionsof the fiber as viewed in section, and in the example of FIG. 4, theultraviolet radiating material is mixed in ring form 1a to constitutethe outermost layer of the fiber as viewed in section. In the figures,hatching represents regions in which the ultraviolet radiating materialis mixed, reference numeral 1 denotes the fiber, 2 denotes the baseprotective layer, and 3 denotes the layer of photocatalyticsemiconductor particles.

The peak wavelength of light that the polyester fiber absorbs is at 318nm, and accordingly, the peak wavelength of light that the layer oftitanium oxide particles absorbs is adjusted to 480 nm. The wavelengthband of light that "LUMINOVA" radiates is, on the other hand, adjustedto 440 to 530 nm.

FIG. 5 is a sectional view of a twisted yarn constituted by naturalfibers and synthetic resin fibers admixed with the ultraviolet radiatingmaterial, and illustrates a means of imparting light storage capacity toa woven fabric using natural fibers.

The following describes the experimental results as to the effect of thephotocatalytic function observed when the photocatalytic sheets obtainedaccording to Examples 1 and 2 were irradiated with ultraviolet rays.

[Prepared Sheets] (size: 10×cm)

a. Woven fabric "DUFY" (100% cotton) treated according to Example 2.

b. Woven fabric "DEOLIA" (50% cotton and 50% polyester) treatedaccording to Example 2.

c. Nonwoven fabric "4880C" (polyester and rayon with acrylic binder)treated according to Example 1.

d. Nonwoven fabric "7870" (polyester; manufactured by Shinwa Co. Ltd.)treated according to Example 1.

e. Nonwoven fabric "7330GP" (polyester and rayon; manufactured by ShinwaCo. Ltd.) treated according to Example 1.

f. Nonwoven fabric "7230CG" (cotton; manufactured by Shinwa Co. Ltd.)treated according to Example 1.

[Experimental Device]

Six small vessels made of polypropylene (each having a square receivingportion of 14×14×3 cm).

A large vessel made of float glass (having a rectangular receivingportion of 62×42×42 cm and a cover made of float glass).

Two black-light lamps (20 W).

A required amount of colored water [POLLUX BLUE (PM-1); from SumikaColor Co., Ltd.], a nonionic 0.04% solution having pH 5.5 to 6.5 andcontaining 0.014% active ingredient.

[Experimental Procedure]

As shown in FIGS. 6 and 7, the large vessel 4 was placed on a desk, andthe black-light lamps 5 were horizontally arranged immediately above thevessel at a distance of 70 mm from the top face of the desk. The sixsmall vessels 6 were arranged inside the large vessel 4 at regularintervals, and the sheets 7 prepared as mentioned above were placed inthe respective small vessels. Then, 50 cc of the colored water waspoured into each of the small vessels 6. With the large vessel 4 closedwith the cover, the vessels and the sheets were left to stand at roomtemperature, and change in color of the colored water in the individualsmall vessels was observed from outside.

POLUX BLUE is a pigment of polymeric organic compound and is decomposedby the photocatalytic function of the photocatalytic semiconductor, sothat it loses the function of coloring the solution. It is thereforepossible to know the degree of progress of the oxidation-reductioncaused by the photocatalytic function as well as the strength of thephotocatalytic function.

[Results]

    ______________________________________                                        First Testing                                                                 Elapsed                                                                       Time   Status                                                                 ______________________________________                                         2 hours                                                                             No change was observed.                                                 4 hours                                                                             Decomposition product of the coloring matter deposited on                     the bottom was observed, and the coloring of each small                       vessel was obviously lightened.                                         6 hours                                                                             No particular change was observed.                                      8 hours                                                                             The coloring of the small vessels in which Sheets a and b                     had been placed appeared to be slightly lighter than that of                  the other small vessels.                                               10 hours                                                                             The coloring of the small vessels in which Sheets a and b                     had been placed was obviously lighter than that of the                        other small vessels. The coloring of Specimens c and d                        was the second lightest.                                               24 hours                                                                             Almost no coloring was observed in respect of the liquid in                   the small vessels in which Sheets a and b had been placed.                    For Specimens a and b, all POLUX BLUE was judged to                           be decomposed, and thus decomposition was completed.                          For the other specimens, slight coloring was observed.                        The coloring of Specimen e was darker than that of                            Specimen f.                                                            26 hours                                                                             The liquid in all small vessels became colorless. For all                     specimens, decomposition was completed.                                ______________________________________                                    

Second Testing

The sheets a to f used in the first testing were washed, and experimentwas conducted following the same procedure. In this case, 50 cc of POLUXBLUE colored liquid was poured afresh into each of the small vessels.

    ______________________________________                                        Elapsed                                                                       Time   Status                                                                 ______________________________________                                         2 hours                                                                             Decomposition considerably advanced. For Specimens a,                         b and c, deposit was observed, revealing that the                             photocatalytic function was not deteriorated even after the                   washing.                                                               21 hours                                                                             The liquid in all small vessels became colorless, and thus                    decomposition of POLUX BLUE was completed.                             ______________________________________                                    

Third Testing

The sheets b, e and f used in the second testing were again washed, 50cc of POLUX BLUE colored liquid was poured afresh into each smallvessel, and experiment was conducted again following the same procedure.The small vessels contained in the large vessel were three in number.

    ______________________________________                                        Elapsed                                                                       Time   Status                                                                 ______________________________________                                         2 hours                                                                             The degree of coloring of all small vessels was found to be                   small, but the change observed could not be called large.               6 hours                                                                             For all of the small vessels, the degree of coloring was                      considerably small. The advance of decomposition                              appeared to be the same for all specimens.                             20 hours                                                                             For all of the small vessels, only slight coloring was                        observed.                                                              24 hours                                                                             No coloring was observed in respect of all small vessels,                     and thus decomposition was completed.                                  ______________________________________                                    

The foregoing reveals that, although the sheets have different strengthsof photocatalytic function, that is, (a, b)>(c, d)>f>e, they all exhibitsufficient oxidation-reduction effect.

According to the present invention, the protective layer constituted bynoncrystalline titanium peroxide particles or inactivated titanium oxideparticles is formed on the surface of the base. Accordingly, even if aphotocatalytic semiconductor layer is formed on the surface of a base ofnatural fibers or synthetic resin fibers containing polymeric organiccompound, the base is not decomposed by the photocatalytic function ofthe photocatalytic semiconductor, and thus is not deteriorated.Consequently, the sheet can be used for a long term as a photocatalyticsheet.

In the case where the base is admixed with an ultraviolet radiatingmaterial, moreover, the function of the photocatalytic sheet can beobtained even in a dark place where no ultraviolet rays reach. Thiscapacity is useful when the sheet is used in filters or medical articleswhich are normally used at locations where ultraviolet rays are unlikelyto reach. Also, since ultraviolet rays do not deteriorate the basecontaining polymeric organic compound, the photocatalytic sheet isimproved in durability.

What is claimed is:
 1. A photocatalytic sheet comprising:a base having apart made of polymeric organic compound; a base protective layer formedon a surface of said part made of polymeric organic compound in saidbase, for intercepting photocatalytic function; and a photocatalyticsemiconductor layer formed on an entire surface of said base includingsaid base protective layer.
 2. A photocatalytic sheet according to claim1, said base including a material selected from the group consisting ofa fiber, a filament, a yarn made of fibers or filaments, a ribbon, aknitted fabric, a woven fabric, a nonwoven fabric, and a film made ofsynthetic resin.
 3. A photocatalytic sheet according to claim 1, saidbase protective layer comprising noncrystalline titanium peroxideparticles.
 4. A photocatalytic sheet according to claim 1, said baseprotective layer comprising titanium oxide particles inactivated withrespect to the photocatalytic function.
 5. A photocatalytic sheetaccording to claim 1, said photocatalytic semiconductor layer comprisingtitanium oxide particles.
 6. A photocatalytic sheet according to claim1, said base retaining a spontaneous emission-type ultraviolet radiatingmaterial.
 7. The photocatalytic sheet according to claim 6, whereinrespective compositions of said ultraviolet radiating material and saidphotocatalytic semiconductor layer are adjusted so that a peak region ofwavelength spectrum of light radiated from said ultraviolet radiatingmaterial is shifted from a peak region of wavelength spectrum of lightto be absorbed by said polymeric organic compound, and overlaps at leastin part with a peak region of light absorption spectrum of saidphotocatalytic semiconductor layer.
 8. A photocatalytic sheet accordingto claim 1, said base retaining a light storage-type ultravioletradiating material.